Slope Stability Report · EXE22/0013

5.0 GEOTECHNICAL INVESTIGATION
5.1       Fieldwork

Two (2) bore holes were undertaken across the site using a power auger mounted to the rear of a
4WD utility to a maximum depth of 2.1 metres. Dynamic Cone Penetrometer (D.C.P) tests were
undertaken at the time of the site investigation. The bore holes were drilled using solid flight augers
fitted with a steel ‘V’ shaped bit or tungsten carbide bit.

An authorised representative from STA Consulting Engineers set out the bore holes locations from
existing site features, directed sampling and logged bore hole profiles. Engineering logs of the bore
holes are presented in Appendix A, together with Explanation Sheets defining the terms and symbols
used in the preparation of the logs.

5.2       Subsurface Conditions

The sequence encountered by the bore holes typically included a loose silty sand overlying a
medium dense sand for the extent of the bore holes undertaken. The following table is a summary
of the subsurface profiles observed:‐
Bore Hole Summary
  Bore        Silty Sand (m)         Sand (m)              Termination Depth
  Hole #                                                   (m)
  BH # 1            0.0 ‐ 0.3              0.3 ‐ 2.1              2.1 m
  BH # 2            0.0 ‐ 0.2              0.2 ‐ 1.6              1.6 m

5.3       Groundwater
Groundwater was not identified at the time of the subsurface investigation. It must be noted that
ground moisture and ground water depths are typically influenced by climatic conditions and the
permeability of the soils observed and may vary with seasonal change.


6.0 SLOPE STABILITY ASSESSMENT
6.1       Stability Assessment Findings
At the time of the site assessment, the following observations were made:‐

         Situated between a prominent sand ridge to the East and a rounded sand dune/ hill to the
          West, topographically the site is positioned mid to lower slope.
         The predominate land shape is concave.
         The natural slope conditions had been altered in order to accommodate the existing
          residence. However taking into consideration surrounding features, the natural unaltered
          slope is assessed as being moderate with a general cross fall sloping roughly from South to
          North estimated at approximately 3 to 5 degrees, increasing in fall further to the North of
          the property particularly where the development abuts the National Park.
         From visual assessment only, it appears that the original earthworks have involved cut and
          filling of the site in order to create a level property. Timber type retaining walls have been
          used to support cut and fill batters. A number of these walls have reached or exceeded their
          expected service life with rotation and deterioration of the timbers evident.
         The site is connected to the mains storm water and sewer networks; therefore outflows are
          to be directed to these mains.
         No ground water or surface water seepage was observed, nor was any vegetation such as
          reeds/ sedge grasses typically associated with wet areas identified.